In certain vehicles such as personnel carriers commonly used for military and paramilitary purposes, such vehicles are subject to upsetting forces often caused by explosions of land mines, grenades, missiles, mortar rounds and gunfire. Under such conditions, it has been found that the principal causes of injury to the occupants of such vehicles has been the upwardly directed forces imposed on the occupants from an explosion at ground level, often hurling the occupants upwardly and perhaps colliding with the roofs of such vehicles, and the downwardly directed forces imposed as the result of the fall of such vehicles following their upward surge caused by the explosion. Typically, such occupants are intended to provide against such movements by the use of restraint systems but such systems alone have been found to be insufficient to prevent the forces of impact causing injury. Accordingly, it is the principal object of the present invention to provide a seat assembly for an occupant of a vehicle subject to upsetting or capsizing forces such as those caused by explosions of land mines and the like which will function to counteract such forces and thus minimize if not eliminate injury to such occupants under such circumstances.